Semiconductor devices having regions of induced high and low conductivity, and methods of making the same

ABSTRACT

Semiconductor apparatus comprising: a substrate having a substrate surface; a layer of a first material overlying a first region of the substrate surface; a layer of a semiconductor overlying the layer of first material and overlying a second region of the substrate surface; a first region of the layer of semiconductor, overlying the layer of first material and having a first conductivity; a second region of the layer of semiconductor, overlying the second region of the substrate surface and having a second conductivity; and the first conductivity being substantially different from the second conductivity. Such semiconductor apparatus further comprising a layer of a second material overlying the second region of the substrate surface, the second region of the layer of semiconductor overlying the layer of the second material.

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owners to licenseothers on reasonable terms as provided for by the terms of AdvancedTechnology Program Cooperative Agreement No. 70NANB2H3032 awarded by theNational Institute of Standards and Technology.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices and circuitscontaining semiconductor devices.

TECHNICAL BACKGROUND OF THE INVENTION

Semiconductor devices are typically formed as multilayer structures inwhich the semiconductor materials are present in a patterned array thatdefines channels for the transport of charge carriers. For example, aninorganic semiconductor layer may be applied to a dielectric substratesurface. A mask may then be applied to protect regions of thesemiconductor layer, intended to constitute charge carrier channels,from a subsequently applied etchant. The etchant then removes thesemiconductor in the unmasked regions, leaving behind a finely patternedarray of semiconductor channels on the substrate. In the absence of suchpatterning, the semiconductor devices may be inoperable or be subject toexcessive crosstalk.

Inorganic semiconductors typically are rigid and brittle at ambienttemperatures. Hence, semiconductor devices formed with inorganicsemiconductors generally are rigid as well. As the myriad end useapplications for semiconductor devices have evolved, availability ofsemiconductor devices that can be flexed and bent without damage isdesirable. Flexible semiconductor device structures also offer potentialcapability for bulk processing in the fabrication of large area devicearrays, such as a continuous web for example, at low unit costs.

Much work has been done to develop organic semiconductors forapplications where flexible semiconductor devices are needed. However,organic semiconductors generally cannot survive the harsh conditionsrequired in order to carry out an etching step to generate a patternedarray of channels for charge carrier transport. Printing processes haveaccordingly been sought in order to directly provide a patternedsemiconductor channel array without a need to remove regions of acontinuous layer of material. Unfortunately, the fine feature definitionthat is needed to generate microarrays of semiconductor channels has notbeen attained by printing of organic semiconductors.

Pentacene, for example, has become an organic semiconductor of greatinterest due to its high conductivity when formed into a crystallinefilm. Single dendritic crystals of pentacene having dimensions as largeas 2 millimeters long, 1 millimeter wide, and 0.5 millimeter thick havebeen produced. For example, individual thin film field effecttransistors comprising single pentacene crystals have been made withhigh channel mobilities within a range of between about 1 centimetersquared per volt-second (cm²/Vs) and about 5 cm²/Vs, at roomtemperature. However, these individual thin film field effecttransistors often have low on/off current ratios, and are not integratedinto a circuit.

Pentacene is known to have high conductivity when formed on substratescomprising poly(vinylphenol). However, direct patterning of pentaceneleads to poorly defined and irregular channel boundaries that cannot beused in fabricating semiconductor devices such as transistors or arrayscomprising transistors.

One effort to generate a suitably patterned array of semiconductorchannels comprising pentacene involved the direct printing of apentacene precursor, which was then converted into pentacene. See, forexample, Dimitrakopoulos et al. U.S. Pat. No. 5,981,970, entitled,“Thin-film field-effect transistor with organic semiconductor requiringlow operating voltages.” However, the performance of semiconductordevices made by this process was unsatisfactory. For example, theprocess required a high temperature annealing step that degraded thesemiconductor devices. Further, two different material patterningmethods were needed. The stability of the resulting semiconductordevices was also unreliable.

Another process for forming devices utilizing patterned organicsemiconductor films, disclosed in Katz U.S. Pat. No. 6,403,397 issued onJun. 11, 2002 and entitled “Process For Fabricating OrganicSemiconductor Device Involving Selective Patterning,” involved treatinga surface to selectively provide regions of greater affinity and lesseraffinity for an organic semiconductor or an organic semiconductorsolution. When the organic semiconductor, or solution comprising thesemiconductor, was deposited on the treated surface, either the organicsemiconductor or the organic semiconductor solution dewetted from thelesser affinity regions or the resultant film adhered only weakly to thelesser affinity regions such that selective removal was readilyperformed. Even where such removal was not performed, the portions ofthe organic semiconductor film overlying the greater affinity regionsexhibited higher conductivity and better film continuity relative to theother portions of the film.

There remains a need for semiconductor devices comprising semiconductorshaving finely patterned regions of high and low conductivity. Therefurther is a need for methods of making semiconductor devices employingsemiconductors that are not easily patterned.

SUMMARY OF THE INVENTION

The present invention provides semiconductor apparatus in which regionsof high and low conductivity are induced in a semiconductor by regionsof materials placed in contact with the semiconductor, and methods ofmaking such semiconductor apparatus. Exemplary embodiments employorganic semiconductors and utilize polymers as such materials.Semiconductor devices can be made with organic and inorganicsemiconductors according to the present invention without patternedplacement or removal of the semiconductors.

In one embodiment according to the present invention, a semiconductorapparatus is provided, comprising: a substrate having a substratesurface; a layer of a first material overlying a first region of thesubstrate surface; a layer of a semiconductor overlying the layer offirst material and overlying a second region of the substrate surface; afirst region of the layer of semiconductor, overlying the layer of firstmaterial and having a first conductivity; a second region of the layerof semiconductor, overlying the second region of the substrate surfaceand having a second conductivity; and the first conductivity beingsubstantially different from the second conductivity.

In another embodiment according to the present invention, such asemiconductor apparatus is provided, further comprising a layer of asecond material overlying the second region of the substrate surface,the second region of the layer of semiconductor overlying the layer ofthe second material. In an additional embodiment according to thepresent invention, such a semiconductor apparatus is provided in whichthe layer of first material overlies the second region of the substratesurface.

In a further embodiment according to the present invention, such asemiconductor apparatus is provided in which the conductivity in thefirst region of the layer of semiconductor is at least about 100 timesas large as the conductivity in the second region of the layer ofsemiconductor. In another embodiment according to the present invention,such a semiconductor apparatus is provided in which the layer ofsemiconductor comprises crystal grains, and in which the average crystalgrain size within the first region of the layer of semiconductor is atleast about 10 times as large as the average crystal grain size withinthe second region of the layer of semiconductor. In an additionalembodiment according to the present invention, such a semiconductorapparatus is provided in which the layer of semiconductor comprisescrystal grains, and in which the average separation between crystalgrains within the second region of the layer of semiconductor is atleast about 10 times as large as the average separation between crystalgrains within the first region of the layer of semiconductor.

In a further embodiment according to the present invention, a method ofmaking a semiconductor apparatus is provided, comprising the steps of:providing a substrate having a substrate surface; providing a layer of afirst material overlying a first region of the substrate surface; andproviding a layer of a semiconductor overlying the layer of firstmaterial and overlying a second region of the substrate surface; a firstregion of the layer of semiconductor, overlying the layer of firstmaterial and having a first conductivity; a second region of the layerof semiconductor, overlying the second region of the substrate surfaceand having a second conductivity; and the first conductivity beingsubstantially different from the second conductivity.

In another embodiment according to the present invention, such a methodof making a semiconductor apparatus is provided, further comprising thestep of providing a layer of a second material overlying the secondregion of the substrate surface, the second region of the layer ofsemiconductor overlying the layer of the second material. In anadditional embodiment according to the present invention, such a methodof making a semiconductor apparatus is provided, in which the layer offirst material overlies the second region of the substrate surface.

In further embodiments according to the present invention, integratedcircuits comprising semiconductor apparatus, and methods for making suchintegrated circuits, are provided.

A more complete understanding of the present invention, as well asfurther features and advantages of the invention, will be apparent fromthe following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from reading thefollowing description of non-limiting embodiments, with reference to theattached drawings, wherein below:

FIG. 1 shows an exemplary embodiment of two thin film transistorsaccording to the present invention;

FIG. 2 shows a further view of the exemplary embodiment of two thin filmtransistors of FIG. 1;

FIG. 3 shows another exemplary embodiment of two thin film transistorsaccording to the present invention;

FIG. 4 shows a further view of the exemplary embodiment of two thin filmtransistors of FIG. 3;

FIG. 5 shows an additional exemplary embodiment of two thin filmtransistors according to the present invention;

FIG. 6 shows a further view of the exemplary embodiment of two thin filmtransistors of FIG. 5;

FIG. 7 shows a further exemplary embodiment of two thin film transistorsaccording to the present invention;

FIG. 8 shows a further view of the exemplary embodiment of two thin filmtransistors of FIG. 7;

FIG. 9 shows a further exemplary embodiment according to the presentinvention of two thin film transistors;

FIG. 10 shows a further view of the exemplary embodiment of two thinfilm transistors of FIG. 9;

FIG. 11 shows an exemplary method according to the present invention ofmaking the transistors shown in FIGS. 1 and 2;

FIG. 12 shows an exemplary method according to the present invention ofmaking the transistors shown in FIGS. 3 and 4;

FIG. 13 shows an exemplary method according to the present invention ofmaking the transistors shown in FIGS. 5 and 6;

FIG. 14 shows an exemplary method according to the present invention ofmaking the transistors shown in FIGS. 7 and 8;

FIG. 15 shows an exemplary method according to the present invention ofmaking the transistors shown in FIG. 9;

FIG. 16 shows an exemplary method according to the present invention ofmaking the transistors shown in FIG. 10; and

FIG. 17 shows Table 1, reporting the results of a series of trials thatwere carried out to fabricate transistors according to exemplaryembodiments of the invention.

The drawings of this specification are not to scale but are merelyschematic representations, and thus are not intended to portray thespecific dimensions of the various embodiments according to theinvention, which may be determined by skilled artisans throughexamination of the disclosure herein.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which several presently preferredembodiments of the invention are shown. This invention may, however, beembodied in various forms and should hot be construed as being limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.

The present invention provides active semiconductor devices, in whichregions of relatively high and relatively low conductivity are inducedin the semiconductor by a selected adjacent layer.

FIG. 1 shows an exemplary embodiment 100, according to the presentinvention, of two thin film transistors generally indicated at 102 and104. Thin film transistor 102 comprises a source electrode 106 and adrain electrode 108 in a spaced apart arrangement overlying asemiconductor layer 110. The subsurface location of a gate electrode 112for thin film transistor 102 under the semiconductor layer 110 is alsoshown. Thin film transistor 104 comprises a source electrode 114 and adrain electrode 116 in a spaced apart arrangement overlying thesemiconductor layer 110. The subsurface location of a gate electrode 118for thin film transistor 104 under the semiconductor layer 110 is alsoshown. Thin film transistors 102 and 104 are further provided with highconductivity inducing layer regions 120 and 122 respectively, thesubsurface locations of which under the semiconductor layer 110 areshown.

FIG. 2 shows a further view of the exemplary embodiment 100 according tothe present invention of thin film transistors 102 and 104, taken online 2-2 in FIG. 1. The gate electrodes 112 and 118 overlie aninsulating substrate 124 in a spaced apart arrangement. Highconductivity inducing layer regions 120 and 122 overlie the insulatingsubstrate 124 and cover gate electrodes 112 and 118, respectively. Thesemiconductor layer 110 overlies the insulating substrate 124 and thehigh conductivity inducing layer regions 120 and 122. The sourceelectrode 106 and drain electrode 108 of thin film transistor 102overlie the semiconductor layer 110 in a spaced apart arrangement inalignment over the gate electrode 112. The source electrode 114 anddrain electrode 116 of thin film transistor 104 overlie thesemiconductor layer 110 in a spaced apart arrangement in alignment overthe gate electrode 118. The source electrodes 106 and 114, drainelectrodes 108 and 116, and the gate electrodes 112 and 118 are incommunication with an electrical circuit, not shown, of which thin filmtransistors 102 and 104 form a part.

The terms “overlying”, “overlies”, “overlie” and the like as used in thepresent specification mean and refer to the relative orientation of thesubject structural elements to each other, which elements may either bein direct mutual contact or may be separated by additional interposedelements as in context are indicated. For example, designated regions ofexemplary semiconductor layer 110 may overlie and be in direct contactwith exemplary insulating substrate 124. Alternatively, designatedregions of exemplary semiconductor layer 110 may overlie exemplaryinsulating substrate 124, but be separated from direct contact with suchsubstrate by interposed exemplary high conductivity inducing layerregion 120 or 122. Analogous structures, for example, compriseinterposed exemplary low conductivity inducing layer regions, asdiscussed below.

In one exemplary embodiment according to the present invention, thesemiconductor layer 110 is formed by an organic semiconductor. Organicsemiconductors are compounds comprising hydrocarbon moieties, andcompositions comprising such compounds, that can be formed into astructure that is capable of transporting charge carriers. Pentacene isone specific exemplary organic compound that is capable of sotransporting charge carriers. Exemplary embodiments according to thepresent invention will be discussed in the context of pentacene as anorganic semiconductor. However, it will be understood that the teachingsaccording to the present invention likewise extend to other organicsemiconductors as well as to inorganic semiconductors, and to mixed andhybrid organic and inorganic semiconductors.

Conductivity in an organic semiconductor is dependent upon itscrystallinity. Electrical conductivity is given by the formula σ=enμ_(d)where μ_(d) is the electron mobility, e is the charge on the electron,and n is the density of free electrons. Conductivity accordingly isproportional to mobility. Mobility can readily be measured. For example,a polycrystalline film of pentacene provides a low mobility, within arange between about 0.3×10 ⁻⁷ cm²/Vs and about 1.5×10⁻⁵ cm²/Vs at roomtemperature. In contrast, where crystallization of pentacene isencouraged as by its thermal evaporation in a vacuum or by growing apentacene film from the vapor phase in a stream of inert gas, mobilitieswithin a range between about 1 cm²/Vs and about 5 cm²/Vs at roomtemperature can be achieved.

Conductivity in an organic semiconductor depends on the size andseparation of crystal grains. The size distribution of crystal grainsdetermines how many of them must be effectively traversed by a chargecarrier in order to be transported from an origin to a destination. Theseparation between crystal grains determines the impact of noncrystalline regions on conductivity. For example, crystal grainsseparated by a distance greater than the tunneling limit for aparticular material may constitute a nonconductive pathway for chargecarriers. The tunneling limit is that distance, determined by theuncertainty principle of quantum mechanics, across which molecules maymove over time in relation to each other without application of externalforces.

Conductivity within a crystal grain of an organic semiconductor dependson charge carrier energy levels and molecular overlaps in the crystal.Energy levels of charge carriers at the boundaries between adjacentcrystals along a pathway cannot interpose undue burdens to the transportof charge carriers.

Referring to FIG. 2, high conductivity inducing layer regions 120 and122 are formed of dielectric materials that increase the conductivity ofthe semiconductor layer 110 in the semiconductor regions 126 and 128aligned over gate electrodes 112 and 118, respectively. This increasedconductivity results from induced crystalline grain growth withinregions 126 and 128 of the semiconductor layer 110. At a molecularlevel, the high conductivity inducing layer regions 120 and 122 areformed of a material having a structure that constitutes an effectivesupport for a crystalline lattice form of the selected semiconductor.Increased conductivity of the semiconductor layer 110 in thesemiconductor region 126 results in increased transconductivity betweenthe source electrode 106 and the drain electrode 108 of thin filmtransistor 102. Increased conductivity of the semiconductor layer 110 inthe semiconductor region 128 results in increased transconductivitybetween the source electrode 114 and the drain electrode 116 of thinfilm transistor 104. Hence, the semiconductor layer 110 is depositedover the high conductivity inducing layer regions 120 and 122 with anincreased degree of crystalline lattice order. This enhancedtransconductivity increases the capacity of the thin film transistors102 and 104 to transport charge carriers, thus directly improving theperformance of such thin film transistors 102 and 104. The conductivitywithin regions of the semiconductor layer 110 surrounding thesemiconductor regions 126 and 128 is relatively unaffected by thepresence of high conductivity inducing layer regions 120 and 122. Thecapability of such regions of the semiconductor layer 110 to transportcharge carriers accordingly is relatively unaffected, leading to reducedcrosstalk through the semiconductor layer 10 between thin filmtransistors 102 and 104.

In one exemplary embodiment according to the present invention, thesemiconductor layer 110 shown in FIGS. 1 and 2 is formed from pentaceneand has a thickness t, indicated at 130, that is within a range ofbetween about 10 pentacene molecules and about 20 pentacene molecules.This semiconductor layer 110 can be conceptualized as including betweenabout 10 layers of pentacene molecules and about 20 layers of pentacenemolecules in a stacked arrangement spanning the thickness t. Pentacenedeposited at the interface 132 between high conductivity inducing layerregion 120 and semiconductor layer 110 accordingly is induced to haveincreased crystal grain size. Similarly, pentacene deposited at theinterface 134 between high conductivity inducing layer region 122 andsemiconductor layer 10 accordingly is induced to have increased crystalgrain size. Increased crystal grain size at the interfaces 132 and 134leads to increased crystal grain size, although to a lesser degree, upthrough the thickness t of the semiconductor layer 10 in a directiontoward the surface regions 136 and 138, respectively.

In operation of the thin film transistor 102, a voltage applied to thegate electrode 112 can be used to control a flow of charge carriersbetween the source electrode 106 and the drain electrode 108. Similarly,in operation of the thin film transistor 104, a voltage applied to thegate electrode 118 can be used to control a flow of charge carriersbetween the source electrode 114 and the drain electrode 116. In thinfilm transistor 102, charge carriers are transported between the sourceelectrode 106 and the drain electrode 108 through the several layers ofpentacene molecules nearest the interface 132 between the highconductivity inducing layer region 120 and the semiconductor layer 110.Similarly in thin film transistor 104, charge carriers are transportedbetween the source electrode 114 and the drain electrode 116 through theseveral layers of pentacene molecules nearest the interface 134 betweenthe high conductivity inducing layer region 122 and the semiconductorlayer 110. Although these several layers of pentacene moleculestypically are not monocrystalline, they nevertheless have substantiallyincreased grain size and substantially reduced grain separation ascompared with a pentacene film deposited directly onto a conventionalinsulating substrate.

FIG. 3 shows another exemplary embodiment 300 according to the presentinvention, of two thin film transistors generally indicated at 302 and304. Thin film transistor 302 comprises a source electrode 306 and adrain electrode 308 in a spaced apart arrangement overlying asemiconductor layer 310, the latter shown in FIG. 4 discussed below. Thesubsurface location of a gate electrode 312 for thin film transistor 302under the semiconductor layer 310 is also shown. Thin film transistor304 comprises a source electrode 314 and a drain electrode 316 in aspaced apart arrangement overlying the semiconductor layer 310. Thesubsurface location of a gate electrode 318 for thin film transistor 304under the semiconductor layer 310 is also shown. The subsurfacelocations of gate dielectric regions 326 and 330 are shown, respectivelyextending throughout overlap regions 301 and 303. Thin film transistors302 and 304 are further provided with low conductivity inducing layer320, also extending throughout overlap regions 301 and 303. Thesubsurface location of low conductivity inducing layer 320 under thesemiconductor layer 310 is shown to cover the surface area underlyingthe thin film transistors 302 and 304 except for those regions of suchsurface, beyond overlap regions 301 and 303, that are covered by thegate dielectric regions 326 and 330. Thus, the low conductivity inducinglayer 320 overlaps throughout overlap regions 301 and 303 with the gatedielectric regions 326 and 330.

FIG. 4 shows a further view of the thin film transistors 302 and 304,taken on line 4-4 in FIG. 3. The gate electrodes 312 and 318 overlie aninsulating substrate 324 in a spaced apart arrangement. Low conductivityinducing layer regions 321, 322 and 323, collectively constituting lowconductivity inducing layer 320 shown in FIG. 3, overlie and coverportions of the insulating substrate 324. A gate dielectric layer 326overlies the insulating substrate 324 and covers the gate electrode 312within the semiconductor region 328 over which the source electrode 306and the drain electrode 308 of thin film transistor 302 are positioned.The locations of the low conductivity inducing layer regions 321 and 322minimize any interpositioning of the low conductivity inducing layer 320between the insulating substrate 324 and the semiconductor layer 310within the semiconductor region 328. The locations of the lowconductivity inducing layer regions 321 and 322 also maximize theinterpositioning of the low conductivity inducing layer 320 between theinsulating substrate 324 and the semiconductor layer 310 outside of thesemiconductor region 328. A gate dielectric layer 330 overlies theinsulating substrate 324 and covers the gate electrode 318 within thesemiconductor region 332 over which the source electrode 314 and thedrain electrode 316 of thin film transistor 304 are positioned. Thelocations of the low conductivity inducing layer regions 322 and 323minimize any interpositioning of the low conductivity inducing layer 320between the insulating substrate 324 and the semiconductor layer 310within the semiconductor region 332. The locations of the lowconductivity inducing layer regions 322 and 323 also maximize theinterpositioning of the low conductivity inducing layer 320 between theinsulating substrate 324 and the semiconductor layer 310 outside of thesemiconductor region 332. The gate dielectric layers 326 and 330 asshown in FIG. 4 overlap with the low conductivity inducing layer regions321, 322 and 323. Alternatively, the gate dielectric layers 326 and 330can meet the edges of or not make contact with the low conductivityinducing layer regions 321, 322 and 323. In one exemplary embodimentaccording to the present invention, the gate dielectric layers 326 and330 can be made barely large enough to effectively cover the gateelectrodes 312 and 318. In another exemplary embodiment according to thepresent invention, the gate electrodes 312 and 318 are fabricated from ametal provided with an oxidized surface, and the gate dielectric layers326 and 330 are omitted. For example, the gate electrodes 312 and 318can be fabricated from aluminum, and the exposed surfaces are anodizedto provide them with a dielectric coating. The semiconductor layer 310overlies the insulating substrate 324, the low conductivity inducinglayer regions 321, 322 and 323, and the gate dielectric layers 326 and330. The source electrode 306 and drain electrode 308 of thin filmtransistor 302 overlie the semiconductor layer 310 in a spaced apartarrangement in alignment over the gate electrode 312. The sourceelectrode 314 and drain electrode 316 of thin film transistor 304overlie the semiconductor layer 310 in a spaced apart arrangement inalignment over the gate electrode 318. The source electrodes 306 and314, drain electrodes 308 and 316, and the gate electrodes 312 and 318are in communication with an electrical circuit, not shown, of whichthin film transistors 302 and 304 form a part.

Referring to FIG. 4, regions 321, 322 and 323 of low conductivityinducing layer 320 are formed of dielectric materials that decrease theconductivity of the semiconductor layer 310 outside of the semiconductorregions 328 and 332 aligned over gate electrodes 312 and 318,respectively. This decreased conductivity results from inducedinhibition of crystalline grain growth in the semiconductor layer 310except within the semiconductor regions 328 and 332. At a molecularlevel, the low conductivity inducing layer 320 is formed of a materialhaving a structure or morphology that inhibits deposition of acrystalline lattice form, over large distances, of the selectedsemiconductor. The decreased conductivity of the semiconductor layer 310results in decreased transconductivity outside of the semiconductorregions 328 and 332. Hence, the semiconductor layer 310 is depositedover the low conductivity inducing layer 320 with a decreased degree ofcrystalline lattice order. The capability of the semiconductor layer 310overlying regions 321, 322 and 323 of the low conductivity inducinglayer 320 to transport charge carriers accordingly is reduced. Lowconductivity inducing layer region 322, for example, is interposedbetween the insulating substrate 324 and a region 334 of thesemiconductor layer 310 that is between the drain electrode 308 of thinfilm transistor 302 and the source electrode 314 of thin film transistor304. The reduced capability of region 334 of the semiconductor layer 310to transport charge carriers results in less crosstalk through thesemiconductor layer 310 between thin film transistors 302 and 304. Thecapability of regions 346 and 348 of the semiconductor layer 310 totransport charge carriers is similarly reduced. The conductivity withinregions 328 and 332 of the semiconductor layer 310 is relativelyunaffected by the presence of low conductivity inducing layer region320. Hence, the performance of the thin film transistors 302 and 304 isimproved by reducing crosstalk, without decreasing the capacity of thethin film transistors 302 and 304 to transport charge carriers.

In one exemplary embodiment according to the present invention, thesemiconductor layer 310 shown in FIGS. 3 and 4 is formed from pentaceneand has a thickness t, indicated at 350, that is within a range ofbetween about 20 pentacene molecules and about 30 pentacene molecules.Pentacene deposited at the interface 336 between low conductivityinducing layer region 322 and semiconductor layer 310 accordingly isinduced to have decreased crystal grain size. Pentacene deposited at theexemplary interface 338 between gate dielectric layer 326 andsemiconductor layer 310 within semiconductor region 328, however, isunaffected by the low conductivity inducing layer 320. Decreased crystalgrain size at the exemplary interface 336 leads to decreased crystalgrain size up through the thickness t of the semiconductor layer 310 ina direction toward the surface region 340. Decreased crystal grain sizesimilarly occurs at interfaces 342 and 344.

FIG. 5 shows an additional exemplary embodiment 500, according to thepresent invention, of two thin film transistors generally indicated at502 and 504. Thin film transistor 502 comprises a source electrode 506and a drain electrode 508 in a spaced apart arrangement overlying asemiconductor layer 510, the latter shown in FIG. 6 discussed below. Thesubsurface location of a gate electrode 512 for thin film transistor 502under the semiconductor layer 510 is also shown. Thin film transistor504 comprises a source electrode 514 and a drain electrode 516 in aspaced apart arrangement overlying the semiconductor layer 510. Thesubsurface location of a gate electrode 518 for thin film transistor 504under the semiconductor layer 510 is also shown. Thin film transistors502 and 504 are further provided with high conductivity inducing layerregions 520 and 521 respectively extending throughout overlap regions501 and 503. A low conductivity inducing layer 519 is provided, alsoextending throughout overlap regions 501 and 503. The low conductivityinducing layer 519 covers the surface of the insulating substrate 525shown in FIG. 6 as discussed immediately below except for those regionsof the insulating substrate 525, beyond overlap regions 501 and 503,that are covered by the high conductivity inducing layer regions 520 and521. Thus, the low conductivity inducing layer 519 overlaps throughoutoverlap regions 501 and 503 with the high conductivity inducing layerregions 520 and 521.

FIG. 6 shows a further view of the exemplary embodiment 500 according tothe present invention of thin film transistors 502 and 504, taken online 6-6 in FIG. 5. The gate electrodes 512 and 518 overlie aninsulating substrate 525 in a spaced apart arrangement. Highconductivity inducing layer regions 520 and 521 overlie the insulatingsubstrate 525, and are aligned with and cover gate electrodes 512 and518, respectively. Low conductivity inducing layer regions 522, 523 and524, collectively constituting low conductivity inducing layer 519 shownin FIG. 5, also overlie and cover portions of the insulating substrate525. The locations of the low conductivity inducing layer regions 522and 523 minimize any interpositioning of the low conductivity inducinglayer 519 between the insulating substrate 525 and the semiconductorlayer 510 within the semiconductor region 528. The locations of the lowconductivity inducing layer regions 523 and 524 minimize anyinterpositioning of the low conductivity inducing layer 519 between theinsulating substrate 525 and the semiconductor layer 510 within thesemiconductor region 530. The locations of the low conductivity inducinglayer regions 522, 523 and 524 also maximize the interpositioning of thelow conductivity inducing layer 519 between the insulating substrate 525and the semiconductor layer 510 outside of the semiconductor regions 528and 530. In the exemplary embodiment shown in FIGS. 5 and 6, the highconductivity inducing layer regions 520 and 521 partially overlap thelow conductivity inducing layer 519 at points 532, 534, 536 and 538. Inanother embodiment according to the present invention, such overlappingis omitted. The semiconductor layer 510 overlies the insulatingsubstrate 525, the low conductivity inducing layer regions 522, 523 and524, and the high conductivity inducing layer regions 520 and 521. Thesource electrode 506 and drain electrode 508 of thin film transistor 502overlie the semiconductor layer 510 in a spaced apart arrangement inalignment over the gate electrode 512. The source electrode 514 anddrain electrode 516 of thin film transistor 504 overlie thesemiconductor layer 510 in a spaced apart arrangement in alignment overthe gate electrode 518. The source electrodes 506 and 514, drainelectrodes 508 and 516, and the gate electrodes 512 and 518 are incommunication with an electrical circuit, not shown, of which thin filmtransistors 502 and 504 form a part.

The high conductivity inducing layer regions 520 and 521 are formed ofdielectric materials that increase the conductivity of the semiconductorlayer 510 in the semiconductor regions 528 and 530, respectively. Theresulting enhanced transconductivity increases the capacity of the thinfilm transistors 502 and 504 to transport charge carriers, thus directlyimproving the performance of such thin film transistors 502 and 504.Regions 522, 523 and 524 of low conductivity inducing layer 519 areformed of dielectric materials that decrease the conductivity of thesemiconductor layer 510 outside of the semiconductor regions 528 and530. The resulting decreased conductivity of the semiconductor layer 510results in decreased transconductivity outside of the semiconductorregions 528 and 530. The capability of the semiconductor layer 510overlying regions 522, 523 and 524 of the low conductivity inducinglayer 519 to transport charge carriers accordingly is reduced. Lowconductivity inducing layer region 523, for example, is interposedbetween the insulating substrate 525 and a region 540 of thesemiconductor layer 510 that is between the drain electrode 508 of thinfilm transistor 502 and the source electrode 514 of thin film transistor504. The reduced capability of region 540 of the semiconductor layer 510to transport charge carriers results in less crosstalk through thesemiconductor layer 510 between thin film transistors 502 and 504.Hence, the performance of the thin film transistors 502 and 504 isimproved both by reducing crosstalk and by increasing the capacity ofthe thin film transistors 502 and 504 to transport charge carriers.

In one exemplary embodiment according to the present invention, thesemiconductor layer 510 shown in FIGS. 5 and 6 is formed from pentaceneand has a thickness t, indicated at 542, that is within a range ofbetween about 10 pentacene molecules and about 20 pentacene molecules.Pentacene deposited at the interface 544 between high conductivityinducing layer region 520 and semiconductor layer 510 accordingly isinduced to have increased crystal grain size. Similarly, pentacenedeposited at the interface 546 between high conductivity inducing layerregion 521 and semiconductor layer 510 accordingly is induced to haveincreased crystal grain size. Increased crystal grain size at theinterfaces 544 and 546 leads to increased crystal grain size, althoughto a lesser degree, up through the thickness t of the semiconductorlayer 510 in a direction toward the surface regions 548 and 550,respectively. Pentacene deposited at the interface 552 between lowconductivity inducing layer region 523 and semiconductor layer 510 incontrast, is induced to have decreased crystal grain size. Decreasedcrystal grain growth at the exemplary interface 552 leads to decreasedcrystal grain size up through the thickness t of the semiconductor layer510 in a direction toward the surface region 554. Decreased crystalgrain growth similarly occurs at interfaces 556 and 558.

FIG. 7 shows a further exemplary embodiment 700, according to thepresent invention, of two thin film transistors generally indicated at702 and 704. Thin film transistor 702 comprises a source electrode 706and a drain electrode 708 in a spaced apart arrangement overlying asemiconductor layer 710, shown in FIG. 8 discussed immediately below.The subsurface location of a gate electrode 712 for thin film transistor702 under the semiconductor layer 710 is also shown. Thin filmtransistor 704 comprises a source electrode 714 and a drain electrode716 in a spaced apart arrangement overlying the semiconductor layer 710.The subsurface location of a gate electrode 718 for thin film transistor704 under the semiconductor layer 710 is also shown. Thin filmtransistors 702 and 704 are further provided with high conductivityinducing layer regions 720 and 722 respectively, the subsurfacelocations of which under the semiconductor layer 710 are shown. Lowconductivity inducing layer 726 underlies the high conductivity inducinglayer regions 720 and 722 and covers the entire surface of theinsulating substrate 724 shown in FIG. 6.

FIG. 8 shows a further view of the exemplary embodiment 700 according tothe present invention of thin film transistors 702 and 704, taken online 8-8 in FIG. 7. The gate electrodes 712 and 718 overlie aninsulating substrate 724 in a spaced apart arrangement. Low conductivityinducing layer 726 overlies the insulating substrate 724 and covers gateelectrodes 712 and 718. High conductivity inducing layer regions 720 and722 are interposed between the low conductivity inducing layer 726 andthe semiconductor layer 710, and are aligned with gate electrodes 712and 718, respectively. The semiconductor layer 710 overlies the lowconductivity inducing layer 726 and the high conductivity inducing layerregions 720 and 722. The source electrode 706 and drain electrode 708 ofthin film transistor 702 overlie the semiconductor layer 710 in a spacedapart arrangement in alignment over the gate electrode 712. The sourceelectrode 714 and drain electrode 716 of thin film transistor 704overlie the semiconductor layer 710 in a spaced apart arrangement inalignment over the gate electrode 718. The source electrodes 706 and714, drain electrodes 708 and 716, and the gate electrodes 712 and 718are in communication with an electrical circuit, not shown, of whichthin film transistors 702 and 704 form a part.

The high conductivity inducing layer regions 720 and 722 are formed ofdielectric materials that increase the conductivity of the semiconductorlayer 710 in the semiconductor regions 728 and 730, respectively. Theresulting enhanced transconductivity increases the capacity of the thinfilm transistors 702 and 704 to transport charge carriers, thus directlyimproving the performance of such thin film transistors 702 and 704. Lowconductivity inducing layer 726 makes contact with regions 732, 734 and736 of semiconductor layer 710. Regions 728 and 730 of the semiconductorlayer 710 are protected from such contact by the interposed highconductivity inducing layer regions 720 and 722. Low conductivityinducing layer 726 can be a continuous layer overlying the insulatingsubstrate 724 and covering the gate electrodes 712 and 718, potentiallyproviding added flexibility in fabrication procedures. The lowconductivity inducing layer 726 is formed of dielectric materials thatdecrease the conductivity of the semiconductor layer 710 in regions 732,734 and 736. The resulting decreased conductivity of the semiconductorlayer 710 results in decreased transconductivity in regions 732, 734 and736 of semiconductor layer 710. The capability of regions 732, 734 and736 of the semiconductor layer 710 to transport charge carriersaccordingly is reduced. Hence, the performance of the thin filmtransistors 702 and 704 is improved both by reducing crosstalk and byincreasing the capacity of the thin film transistors 702 and 704 totransport charge carriers.

FIG. 9 shows a further exemplary embodiment 900, according to thepresent invention, of two thin film transistors generally indicated at902 and 904. Thin film transistor 902 comprises a source electrode 906and a drain electrode 908 in a spaced apart arrangement overlying asemiconductor layer 910. Thin film transistor 904 comprises a sourceelectrode 914 and a drain electrode 916 in a spaced apart arrangementoverlying the semiconductor layer 910. Gate electrode 912 overlies aninsulating substrate 925 and is in alignment with a midpoint betweensource electrode 906 and drain electrode 908 of thin film transistor902. Gate electrode 918 overlies the insulating substrate 925 and is inalignment with a midpoint between source electrode 914 and drainelectrode 918 of thin film transistor 904. High conductivity inducinglayer 920 overlies the insulating substrate 925 and covers gateelectrodes 912 and 918. The semiconductor layer 910 overlies highconductivity inducing layer 920. The source electrode 906 and the drainelectrode 908 of thin film transistor 902 overlie region 922 of thesemiconductor layer 910, centered over gate electrode 912. Region 922 ofthe semiconductor layer 910 is in direct contact with the highconductivity inducing layer 920. The source electrode 914 and the drainelectrode 916 of thin film transistor 904 overlie region 924 of thesemiconductor layer 910, centered over gate electrode 918. Region 924 ofthe semiconductor layer 910 is also in direct contact with the highconductivity inducing layer 920. Regions 922 and 924 of thesemiconductor layer are interposed by regions 926, 928 and 930 of thesemiconductor layer 910. Low conductivity inducing layer regions 932,934 and 936 are interposed between the high conductivity inducing layer920 and regions 926, 928 and 930 of the semiconductor layer 910,respectively. The locations of the low conductivity inducing layerregions 932 and 934 minimize any interpositioning of the lowconductivity inducing layer between the high conductivity inducing layer920 and the semiconductor layer 910 within the high conductivitysemiconductor region 922. The locations of the low conductivity inducinglayer regions 934 and 936 minimize any interpositioning of the lowconductivity inducing layer between the high conductivity inducing layer920 and the semiconductor layer 910 within the high conductivitysemiconductor region 924. The locations of the low conductivity inducinglayer regions 932, 934 and 936 also maximize the interpositioning of thelow conductivity inducing layer between the high conductivity inducinglayer 920 and the semiconductor layer 910 outside of the highconductivity semiconductor regions 922 and 924. The source electrodes906 and 914, drain electrodes 908 and 916, and the gate electrodes 912and 918 are in communication with an electrical circuit, not shown, ofwhich thin film transistors 902 and 904 form a part.

The high conductivity inducing layer 920 makes direct contact withregions 922 and 924 of semiconductor layer 910. The high conductivityinducing layer 920 is formed of dielectric materials that increase theconductivity of the semiconductor layer 910 in regions 922 and 924. Theresulting increased conductivity of the semiconductor layer 910 resultsin increased transconductivity in regions 922 and 924 of semiconductorlayer 910. High conductivity inducing layer 920 can be a continuouslayer overlying the insulating substrate 925 and covering the gateelectrodes 912 and 918, potentially providing added flexibility infabrication procedures. The low conductivity inducing layer regions 932,934 and 936 are formed of dielectric materials that decrease theconductivity of the semiconductor layer 910 in the low conductivitysemiconductor regions 926, 928 and 930, respectively. The resultingdecreased conductivity of the semiconductor layer 910 results indecreased transconductivity outside of the semiconductor regions 922 and924. The capability of the semiconductor layer 910 in the lowconductivity semiconductor regions 926, 928 and 930 to transport chargecarriers accordingly is reduced. Low conductivity semiconductor region928, for example, is located between the drain electrode 908 of thinfilm transistor 902 and the source electrode 914 of thin film transistor904. Hence, the performance of the thin film transistors 902 and 904 isimproved both by reducing crosstalk and by increasing the capacity ofthe thin film transistors 902 and 904 to transport charge carriers.

FIG. 10 shows a further exemplary embodiment 1000, according to thepresent invention, of two thin film transistors generally indicated at1002 and 1004. Thin film transistor 1002 comprises a source electrode1006 and a drain electrode 1008 in a spaced apart arrangement overlyinga high conductivity semiconductor region 1010. Thin film transistor 1004comprises a source electrode 1012 and a drain electrode 1014 in a spacedapart arrangement overlying a high conductivity semiconductor region1016. A gate electrode 1018 overlies an insulating substrate 1020 and isin alignment with a midpoint between source electrode 1006 and drainelectrode 1008 of thin film transistor 1002. A gate electrode 1022overlies the insulating substrate 1020 and is in alignment with amidpoint between source electrode 1012 and drain electrode 1014 of thinfilm transistor 1004. Low conductivity inducing layer 1024 overlies theinsulating substrate 1020 and covers gate electrodes 1018 and 1022. Thehigh conductivity inducing layer region 1010 overlies the lowconductivity inducing layer 1024 and is centered over gate electrode1018. The high conductivity inducing layer region 1016 overlies the lowconductivity inducing layer 1024 and is centered over gate electrode1022. A semiconductor layer 1026 overlies the low conductivity inducinglayer 1024, the high conductivity inducing layer regions 1010 and 1016,the source electrodes 1006 and 1012, and the drain electrodes 1008 and1014. The high conductivity inducing layer regions 1010 and 1016 are indirect contact with high conductivity regions 1028 and 1030 of thesemiconductor layer 1026, respectively. The low conductivity inducinglayer 1024 is in direct contact with the semiconductor layer 1026 in lowconductivity semiconductor regions 1032, 1034 and 1036. The highconductivity inducing layer regions 1010 and 1016 are formed ofdielectric materials that increase the conductivity of the semiconductorlayer 1010 in regions 1028 and 1030, respectively. The low conductivityinducing layer 1024 is formed of dielectric materials that decrease theconductivity of the semiconductor layer 1010 in the low conductivitysemiconductor regions 1032, 1034 and 1036, respectively. The sourceelectrodes 1006 and 1008, drain electrodes 1012 and 1014, and the gateelectrodes 1018 and 1022 are in communication with an electricalcircuit, not shown, of which thin film transistors 1002 and 1004 form apart.

FIGS. 1-10 as discussed above relate to exemplary and non limitingembodiments according to the present invention. For example, theembodiments shown in FIGS. 1-10 all show two thin film transistors.Other embodiments according to the present invention can comprise anydesired quantity of thin film transistors. For example, the thin filmtransistors can be incorporated into an integrated circuit. Othersuitable designs for thin film transistors can be employed. For example,in one exemplary further thin film transistor design according to thepresent invention, a high conductivity inducing layer is positioned toincrease the conductivity of a semiconductor region that is in contactwith the source and drain electrodes of a thin film transistor. Inanother exemplary further thin film transistor design according to thepresent invention, a low conductivity inducing layer is positioned todecrease the conductivity of a semiconductor region adjacent to asemiconductor region that is in contact with the source and drainelectrodes of a thin film transistor. In an additional exemplary furtherthin film transistor design according to the present invention, a lowconductivity inducing layer is positioned to decrease the conductivityof a semiconductor region that is interposed between semiconductorregions that are in contact with the source and drain electrodes of aplurality of thin film transistors. In another exemplary further thinfilm transistor design according to the present invention, a highconductivity inducing layer is positioned to increase the conductivityof a semiconductor region that is in contact with the source and drainelectrodes of a thin film transistor, and a low conductivity inducinglayer is positioned to decrease the conductivity of a semiconductorregion adjacent to the semiconductor region that is in contact with thesource and drain electrodes of a thin film transistor.

The embodiments shown in FIGS. 1-10 and discussed above are all fieldeffect transistors each employing a single semiconductor layer. Otherfield effect transistor designs comprising two semiconductor layers, forexample, can also be employed. For example, metal oxide semiconductorfield effect transistor (MOSFET) designs, and junction field effecttransistor (JFET) designs can be employed.

Further embodiments according to the invention will be discussed belowin connection with thin film transistors. However, it is to beunderstood that the teachings according to the present invention can befurther extended to devices other than thin film transistors thatrequire lateral patterning of a semiconductor film or layer into regionsof relatively high and low conductivity. For example, diodes can beproduced in an analogous manner. Other exemplary semiconductorelectronic devices that can be fabricated by use of the teachingsaccording to the present invention include light emitting devices,photodetecting devices, photovoltaic cells, photoconductive cells,photoresistive cells, photodiodes, and photoswitches.

Appropriate materials for forming high and low conductivity inducinglayers to be employed in making thin film transistors according to thepresent invention are selected depending upon the composition of thesemiconductor to be employed. Materials for forming high conductivityinducing layers are selected that encourage crystal grain growth in anadjacent layer of the semiconductor. Materials for forming lowconductivity inducing layers are selected that impede and reduce crystalgrain size in an adjacent layer of the semiconductor. Where materialsfor forming high and low conductivity inducing layers are both employed,the affinity of the chosen semiconductor for such respective materialsmay be uniform or different as desired. Affinity is a measure of theability of two materials to bind together, and does not affect crystalgrain growth.

In one embodiment according to the present invention, the selectedsemiconductor is pentacene. Pentacene, an organic compound, is a linearacene having five rings. Films of pentacene are capable oftransconductive transport of holes. Pentacene has the highest mobilityamong the linear acenes. Although the mobility of pentacene inpolycrystalline organic thin films is within a low range between about0.3×10⁻⁷ cm²/Vs and about 1.5×10⁻⁵ cm²/Vs at room temperature, themobility of pentacene in monocrystalline organic thin films is within ahigh range between about 1 cm²/Vs and about 5 cm²/Vs. In anotherembodiment according to the present invention, another linear ornonlinear acene is substituted for pentacene.

Suitable polymers for making layers for use in contact with portions ofan organic semiconductor layer comprising pentacene to induce hightransconductivity include, for example, poly(para-vinyl phenol),poly(4-vinylpyridine), and poly(2-vinylnaphthalene). Poly(para-vinylphenol) is also known as poly(hydroxystyrene). Poly(meta-vinyl phenol)or poly(ortho-vinyl phenol) may also be effective. Alternatively,poly(para-vinyl phenol-co-2-hydroxyethylmethacrylate) can be employed.In addition to poly(4-vinylpyridine), poly(2-vinylpyridine) may also beeffective. In addition to poly(2-vinylnaphthalene),poly(2-vinylnaphthalene-co-2-ethylhexyl acrylate) can be used. Inaddition to poly(2-vinylnaphthalene), poly(1-vinylnaphthalene) may alsobe effective. Blends of these polymers, and of other suitable polymers,if available, can also be used. The term “blends” as used in thisspecification broadly encompasses and includes copolymers formed fromthe corresponding monomers or oligomers, mixtures of polymers, and othercompositions comprising the monomers, however produced.

Suitable polymers for making layers for use in contact with portions ofan organic semiconductor layer comprising pentacene to induce lowtransconductivity include, for example, poly(n-butyl methacrylate),poly(vinylidene difluoride-co-methyl vinyl ether), polystyrene,poly(p-methoxystyrene), poly(vinylidene difluoride), poly(vinylacetate), poly(vinyl propionate) and poly(methoxy acetate). In oneembodiment according to the present invention, poly(vinylidenedifluoride-co-methyl vinyl ether) comprising about 85% by weight ofvinylidene difluoride and about 15% by weight of methyl vinyl ether,having a dielectric constant of about 10, is employed. In addition topoly(n-butyl methacrylate), a polymer such as poly(n-propylmethacrylate), poly(isopropyl methacrylate), or poly(n-pentylmethacrylate) may also be effective. Acrylates, ethacrylates, andhalogenated analogs of poly(n-butyl methacrylate) may further beeffective. In addition to poly(vinylidene difluoride-co-methyl vinylether), a polymer such as poly(vinylidene difluoride-co-ethyl vinylether) or poly(vinylidene difluoride-co-propyl vinyl ether) may beeffective. Blends of these polymers, blends being broadly defined asabove, and of other suitable polymers, if available, can also be used.

In another embodiment according to the present invention, a polymer formaking layers to be placed in contact with portions of an organicsemiconductor layer comprising pentacene to induce low transconductivityis selected for its high content of charge carrier traps. Such apolymer, when interposed between selected regions of a substrate surfaceand an overlying semiconductor layer, effectively reduces theconductivity of those portions of the semiconductor layer overlying theselected regions. For example, poly(dimethylaminoethyl methacrylate),poly(dimethylaminopropyl methacrylate), poly(aminopropyl methacrylate)and poly(diethylaminoethyl methacrylate) can be so used. Each of thesepolymers has a high concentration of amino groups and a glass transitiontemperature approximating that of poly(n-butyl methacrylate). Thepolymers discussed above for making layers that induce high and lowconductivity in films comprising pentacene are commercially availablefrom the Sigma-Aldrich Chemical Company, St. Louis, Mo.

In one embodiment according to the present invention, thin filmtransistors 102 and 104 shown in FIGS. 1 and 2 having pentacenesemiconductor layer 110 are fabricated by an exemplary method 1100 shownin FIG. 11. Referring to FIG. 11, a silicon dioxide glass slide having arough surface to inhibit pentacene crystallization is provided at step1105 to serve as the insulating substrate 124. The rough surface can beprovided, for example, by subjecting a silicon dioxide slide to a basicetch or to abrasion by sandpaper. A surface of the insulating substrate124 on which semiconductor layer 110 and high conductivity inducingregions 120 and 122 will be provided, is thoroughly cleaned. Forexample, the surface of the insulating substrate 124 can be treated bysonication while being immersed in a soap solution, rinsed in a volatilesolvent such as methanol or acetone, blown dry by nitrogen, and thensubjected to an oxygen plasma.

At step 1110, gate electrodes 112 and 118 are provided on the insulatingsubstrate 124. For example, a steel shadow mask can be placed over thesurface of the insulating substrate 124, leaving exposed those portionsof the surface where gate electrodes 112 and 118 are to be located. Theinsulating substrate 124 is then placed in a suitable vacuum chambersuch as a bell jar, which is then evacuated. A source of aluminum metalis also placed in the vacuum chamber and heated to vaporize and depositaluminum over the shadow mask to produce the gate electrodes 112 and118. Other suitable materials for fabricating gate electrodes can besubstituted for aluminum. For example, gold, silver, gallium, indium,platinum, nickel, titanium, copper, or conductive ceramics such asindium tin oxide can be used. Any metal that can be evaporated orsputtered can be used for the gate.

At step 1115, high conductivity inducing layer regions 120 and 122 areprovided on the insulating substrate 124, centered over the gateelectrodes 112 and 118, respectively. A suitable solution of a highconductivity inducing polymer is needed, as the high conductivityinducing polymers discussed above generally are commercially provided ina powder form. For example, a selected polymer such aspoly(4-vinylpyridine) is suitably purified, such as by reprecipitationor chromatography, and dissolved in a suitable solvent. A solutioncomprising between about 5% and about 10% of poly(4-vinylpyridine) inmethyl ethyl ketone, for example, can be prepared. The polymer solutioncan, for example, be applied to the insulating substrate 124 by a spincoating process. A poly(4-vinylpyridine) film is spin coated on theinsulating substrate 124, having a thickness, for example, of about onemicron. The film of poly(4-vinylpyridine) is then removed from theinsulating substrate 124 except for portions to constitute the highconductivity inducing layer regions 120 and 122, for example by a wipingthe polymer away with a swab dipped in methyl ethyl ketone. The gateelectrodes 112 and 118 are then exposed by the same wiping process.

In another embodiment according to the present invention, a laminationprocess is substituted for the spin coating process in order to depositthe high conductivity inducing polymer in step 1115. Suitable laminationprocesses for this purpose are disclosed in U.S. patent application Ser.No. ______, filed concurrently herewith, entitled “Process forLaminating a Dielectric Layer into a Semiconductor.” This patentapplication is assigned to E. I. du Pont de Nemours and Company, docketNo. CL-2181, and is hereby incorporated herein by reference in itsentirety. It is to be understood that such lamination processes can beused in substitution for spin coating processes in all of the instanceswhere spin coating is discussed in this specification.

At step 1120, a layer 110 of pentacene is provided on the highconductivity inducing layer regions 120 and 122, and on the exposedportions of the insulating substrate 124. The pentacene is applied by aprocess that is suitable to allow the high conductivity inducing layerregions 120 and 122 to affect the crystallinity of the appliedpentacene. For example, pentacene can be applied onto the highconductivity inducing layer regions 120 and 122 by employing a vacuumsublimation process. The insulating substrate 124 having the highconductivity inducing layer regions 120 and 122 is placed in a suitablevacuum chamber such as a bell jar, which is then evacuated. A source ofpentacene is also placed in the vacuum chamber and heated to sublimatethe pentacene and deposit a pentacene layer 110 over the highconductivity inducing layer regions 120 and 122 and over the exposedportions of the insulating substrate 124. High conductivity regions 126and 128 are thus generated within the pentacene layer 110.

At step 1125, source electrodes 106 and 114, and drain electrodes 108and 116, are provided on the semiconductor layer 110 in alignment overthe high conductivity inducing layer regions 120 and 122. For example, asteel shadow mask can be placed over the surface of the semiconductorlayer 110, leaving exposed those portions of the surface where thesource electrodes 106 and 114 and the drain electrodes 108 and 116 areto be located. The insulating substrate 124 is then placed in a suitablevacuum chamber such as a bell jar, which is then evacuated. A source ofgold metal is also placed in the vacuum chamber and heated to vaporizeand deposit gold over the shadow mask to produce the source electrodes106 and 114 and the drain electrodes 108 and 116.

In another embodiment according to the present invention, thin filmtransistors 302 and 304 shown in FIGS. 3 and 4 having pentacene layer310 are fabricated by an exemplary method 1200 shown in FIG. 12.Referring to FIG. 12, a silicon dioxide glass slide having a roughsurface to inhibit pentacene crystallization is provided at step 1205 toserve as the insulating substrate 324. A surface of the insulatingsubstrate 324 on which low conductivity inducing layer regions 321, 322and 323 as well as gate dielectric regions 326 and 330 will be provided,is thoroughly cleaned. The surface of the insulating substrate 324 canbe cleaned in the same manner as discussed above in connection with FIG.11.

At step 1210, gate electrodes 312 and 318 are provided on the insulatingsubstrate 324 in the same manner as discussed above in connection withFIG. 11.

At step 1215, low conductivity inducing polymer layer regions 321, 322and 323 are provided on the insulating substrate. A suitable solution ofa low conductivity inducing polymer is needed, as the low conductivityinducing polymers discussed above generally are commercially provided ina powder form. For example, a selected polymer such as poly(n-butylmethacrylate), is dissolved in a suitable solvent. A solution comprisingbetween about 5% and about 10% of poly(n-butyl methacrylate) in methylethyl ketone, for example, can be prepared. The polymer solution can,for example, be applied to the insulating substrate 324 by the same spincoating process that was discussed above in connection with FIG. 11. Apoly(n-butyl methacrylate) film is spin coated on the insulatingsubstrate 324, having a thickness, for example, of about one micron. Thefilm of poly(n-butyl methacrylate) is then removed from the insulatingsubstrate 324 except for portions to constitute the low conductivityinducing layer regions 321, 322 and 323, for example by a wiping thepolymer away with a swab dipped in methyl ethyl ketone. The gateelectrodes 112 and 118 are then exposed by the same wiping process.

In the embodiment shown in FIG. 12 and discussed above, the lowconductivity inducing layer regions 321, 322 and 323 are produced on theinsulating substrate after the gate electrodes 312 and 318 are produced.In further embodiments according to the present invention, step 1215 iscarried out before carrying out step 1210, or the two steps are carriedout simultaneously.

At step 1220, gate dielectric regions 326 and 330 are provided on theinsulating substrate 324. The function of gate dielectric regions 326and 330 is to insulate the gate electrodes from the semiconductor layer310. Accordingly, any organic or inorganic dielectric material that iscompatible with the other materials with which it comes into contact inthin film transistors 302 and 304 can be used. In one exemplaryembodiment according to the present invention, the gate dielectriclayers 326 and 330 can be made barely large enough to effectively coverthe gate electrodes 312 and 318. In another exemplary embodimentaccording to the present invention, the gate electrodes 312 and 318 arefabricated from a metal provided with an oxidized surface, and theoxidized surface serves as gate dielectric layers 326 and 330. Forexample, the gate electrodes 312 and 318 can be fabricated fromaluminum, and the exposed surfaces are anodized to provide them with adielectric coating.

In the embodiment shown in FIG. 12 and discussed above, the gatedielectric regions 326 and 330 are produced on the insulating substrateafter the low conductivity inducing layer regions 321, 322 and 323 areproduced. In further embodiments according to the present invention,step 1220 is carried out before carrying out step 1215, or the two stepsare carried out simultaneously.

At step 1225, a layer 310 of pentacene is provided on the lowconductivity inducing layer regions 321, 322 and 323, on the gatedielectric regions 326 and 330, and on the exposed portions of theinsulating substrate 324. The pentacene can be applied using the sameprocess as discussed above in connection with FIG. 11, in a mannersuitable to allow the low conductivity inducing layer regions 321, 322and 323 to affect the crystallinity of the applied pentacene. Lowconductivity regions 346, 334 and 348 are thus generated within thepentacene layer 310.

At step 1230, source electrodes 306 and 314, and drain electrodes 308and 316, are provided on the semiconductor layer 110 in alignment overthe gate electrodes 312 and 318, respectively. These source electrodes306 and 314, and drain electrodes 308 and 316 can be prepared in thesame manner as was discussed above in regard to FIG. 11.

In another embodiment 1300 according to the present invention, thin filmtransistors 502 and 504 shown in FIGS. 5 and 6 having pentacene layer510 are fabricated by an exemplary method shown in FIG. 13. Referring toFIG. 13, a silicon dioxide glass slide having a rough surface to inhibitpentacene crystallization is provided at step 1305 to serve as theinsulating substrate 524. A surface of the insulating substrate 524 onwhich low conductivity inducing layer regions 522, 523 and 524 as wellas gate electrodes 512 and 518 will be provided, is thoroughly cleaned.The surface of the insulating substrate 524 can be cleaned in the samemanner as discussed above in connection with FIG. 11.

At step 1310, gate electrodes 512 and 518 are provided on the insulatingsubstrate 524 in the same manner as discussed above in connection withFIG. 11.

At step 1315, low conductivity inducing polymer layer regions 522, 523and 524 are provided on the insulating substrate in the same manner asdiscussed above in regard to FIG. 12. In the embodiment shown in FIG.13, the low conductivity inducing layer regions 522, 523 and 524 areproduced on the insulating substrate after the gate electrodes 512 and518 are produced. In further embodiments according to the presentinvention, step 1315 is carried out before carrying out step 1310, orthe two steps are carried out simultaneously.

At step 1320, high conductivity inducing layer regions 520 and 521 areprovided on the insulating substrate 525. The high conductivity inducinglayer regions 520 and 521 may as shown in FIG. 6 partially overlap thelow conductivity inducing layer regions 522, 523 and 524. The highconductivity inducing layer regions 520 and 521 may be prepared in thesame manner as discussed above in connection with FIG. 11.

In the embodiment shown in FIG. 13, the low conductivity inducing layerregions 522, 523 and 524 are produced on the insulating substrate beforethe high conductivity inducing layer regions 520 and 521 are produced.In further embodiments according to the present invention, step 1320 iscarried out before carrying out step 1315, or the two steps are carriedout simultaneously.

At step 1325, a layer 510 of pentacene is provided on the highconductivity inducing layer regions 520 and 521, and on the exposedportions of the low conductivity inducing layer regions 522, 523 and524. The pentacene is applied using the same process as discussed abovein connection with FIG. 11, in such a manner to allow the highconductivity inducing layer regions 520 and 521 as well as the exposedportions of the low conductivity inducing layer regions 522, 523 and 524to affect the crystallinity of the applied pentacene. High conductivityregions 528 and 530 and low conductivity regions 540, 560 and 562 arethus generated within the pentacene layer 510.

At step 1330, source electrodes 506 and 514, and drain electrodes 508and 516, are provided on the semiconductor layer 510 in alignment overthe gate electrodes 512 and 518, respectively. These source electrodes506 and 514, and drain electrodes 508 and 516 can be prepared in thesame manner as was discussed above in regard to FIG. 11.

In another embodiment according to the present invention, thin filmtransistors 702 and 704 shown in FIGS. 7 and 8 having pentacene layer710 are fabricated by an exemplary method 1400 shown in FIG. 14.Referring to FIG. 14, a silicon dioxide glass slide having a roughsurface to inhibit pentacene crystallization is provided at step 1405 toserve as the insulating substrate 724. A surface of the insulatingsubstrate 724 on which a low conductivity inducing layer 726 will beprovided, is thoroughly cleaned in the same manner as discussed above inconnection with FIG. 11.

At step 1410, gate electrodes 712 and 718 are provided on the insulatingsubstrate 724 in the same manner as discussed above in connection withFIG. 11. At step 1415, a low conductivity inducing polymer layer 726 isprovided on the insulating substrate. A suitable solution of a lowconductivity inducing polymer such as poly(n-butyl methacrylate) isprovided in the same manner as discussed above in connection with FIG.12.

The polymer solution can, for example, be applied to the insulatingsubstrate 724 by the same spin coating process discussed above. A filmof poly(n-butyl methacrylate) is spin coated on the insulating substrate124, having a thickness, for example, of about one micron. The film isthen removed from the insulating substrate 124 except for portions toconstitute the low conductivity inducing layer 726, for example by awiping the polymer away with a swab dipped in methyl ethyl ketone.

At step 1420, high conductivity inducing layer regions 720 and 722 areprovided on the low conductivity inducing polymer layer 726. A suitablesolution of a high conductivity inducing polymer such aspoly(4-vinylpyridine), is provided in the same manner as discussed abovein connection with FIG. 11. The polymer solution can, for example, beapplied to the low conductivity inducing polymer layer 726 by the samespin coating process and under the same processing conditions discussedabove in connection with step 1115 of FIG. 11. A film ofpoly(4-vinylpyridine) is spin coated on the low conductivity inducinglayer 726, having a thickness, for example, of about one micron. Thefilm is then removed from the low conductivity inducing layer 726 exceptfor portions to constitute the high conductivity inducing layer regions720 and 722, for example by a wiping the polymer away with a swab dippedin methyl ethyl ketone.

At step 1425, a layer 710 of pentacene is provided on the highconductivity inducing layer regions 720 and 722, and on the exposedportions of the low conductivity inducing polymer layer 726. Thepentacene is applied by the same process as discussed above, in a mannerthat is suitable to allow the high conductivity inducing layer regions720 and 722 as well as the exposed portions of the low conductivityinducing polymer layer 726 to affect the crystallinity of the appliedpentacene. High conductivity regions 728 and 730 and low conductivityregions 732, 734 and 736 are thus generated within the pentacene layer710.

At step 1430, source electrodes 706 and 714 and drain electrodes 708 and716 are provided on the semiconductor layer 710 overlying the highconductivity inducing layer regions 720 and 722. These electrodes mayalso partially overlie the portions of the low conductivity inducingpolymer layer 726 that are in contact with the semiconductor layer 710.The source electrodes 706 and 714 and drain electrodes 708 and 716 canbe prepared in the same manner as was discussed above in regard to FIG.11.

In another embodiment according to the present invention, thin filmtransistors 902 and 904 shown in FIG. 9 having pentacene layer 910 arefabricated by an exemplary method 1500 shown in FIG. 15. Referring toFIG. 15, a silicon dioxide glass slide having a rough surface to inhibitpentacene crystallization is provided at step 1505 to serve as theinsulating substrate 925. A surface of the insulating substrate 925 onwhich a high conductivity inducing layer 920 will be provided, isthoroughly cleaned in the same manner as discussed above in connectionwith FIG. 11.

At step 1510, gate electrodes 912 and 918 are provided on the insulatingsubstrate 925 in the same manner as discussed above in connection withFIG. 11.

At step 1515, a high conductivity inducing polymer layer 920 is providedon the insulating substrate. A suitable solution of a high conductivityinducing polymer such as poly(4-vinylpyridine) is provided in the samemanner as discussed above in connection with FIG. 11. The polymersolution can, for example, be applied to the insulating substrate 925 bythe same spin coating process and under the same processing conditionsdiscussed above in connection with step 1115 of FIG. 11. A film ofpoly(4-vinylpyridine) is spin coated on the insulating substrate 925,having a thickness, for example, of about one micron. The film is thenremoved from the insulating substrate 925 except for portions toconstitute the high conductivity inducing layer 920, for example by awiping the polymer away with a swab dipped in methyl ethyl ketone.

At step 1520, low conductivity inducing layer regions 932, 934 and 936are provided on the high conductivity inducing polymer layer 920. Asuitable solution of a low conductivity inducing polymer such aspoly(n-butyl methacrylate) is provided in the same manner as discussedabove in connection with FIG. 12. The polymer solution can, for example,be applied to the high conductivity inducing polymer layer 920 by thesame spin coating process and under the same processing conditionsdiscussed above in connection with step 1215 of FIG. 12. A film ofpoly(n-butyl methacrylate) is spin coated on the high conductivityinducing layer 920, having a thickness, for example, of about onemicron. The film is then removed from the high conductivity inducinglayer 920 except for portions to constitute the low conductivityinducing layer regions 932, 934 and 936, for example by a wiping thepolymer away with a swab dipped in methyl ethyl ketone.

At step 1525, a layer 910 of pentacene is provided on the lowconductivity inducing layer regions 932, 934 and 936, and on the exposedportions of the high conductivity inducing polymer layer 920. Thepentacene is applied by the same process as discussed above, in a mannerthat is suitable to allow the low conductivity inducing layer regions932, 934 and 936 as well as the exposed portions of the highconductivity inducing polymer layer 920 to affect the crystallinity ofthe applied pentacene. High conductivity regions 922 and 924 and lowconductivity regions 926, 928 and 930 are thus generated within thepentacene layer 910.

At step 1530, source electrodes 906 and 914 and drain electrodes 908 and916 are provided on the semiconductor layer 910 overlying regions of thehigh conductivity inducing polymer layer 920 that are in contact withthe semiconductor layer 910. These electrodes may also partially overlielow conductivity inducing polymer layer regions 932, 934 and 936. Thesource electrodes 906 and 914 and drain electrodes 908 and 916 can beprepared in the same manner as was discussed above in regard to FIG. 11.

In another embodiment according to the present invention, thin filmtransistors 1002 and 1004 shown in FIG. 10 having pentacene layer 1012are fabricated by an exemplary method 1600 shown in FIG. 16. Referringto FIG. 16, a silicon dioxide glass slide having a rough surface toinhibit pentacene crystallization is provided at step 1605 to serve asthe insulating substrate 1024, in the same manner as discussed inconnection with step 1405 of FIG. 14. At step 1610, gate electrodes 1018and 1020 are provided on the insulating substrate 1024 in the samemanner as discussed above in connection with step 1410 of FIG. 14. Atstep 1615, a low conductivity inducing polymer layer 1024 is provided onthe insulating substrate in the same manner as discussed in connectionwith step 1415 of FIG. 14. At step 1620, high conductivity inducinglayer regions 1010 and 1016 are provided on the low conductivityinducing polymer layer 1024 in the same manner as discussed above inconnection with step 1420 of FIG. 14.

At step 1625, source electrodes 1006 and 1012 and drain electrodes 1008and 1014 are provided on the high conductivity inducing layer regions1010 and 1016. The source electrodes 1006 and 1012 and drain electrodes1008 and 1014 can be prepared in the same manner as was discussed abovein regard to FIG. 11.

At step 1630, a layer 1010 of pentacene is provided on the highconductivity inducing layer regions 1010 and 1016, on the sourceelectrodes 1006 and 1012 and drain electrodes 1008 and 1014, and on theexposed portions of the low conductivity inducing polymer layer 1024.The pentacene is applied by the same process as discussed above, in amanner that is suitable to allow the high conductivity inducing layerregions 1010 and 1016 as well as the exposed portions of the lowconductivity inducing polymer layer 1024 to affect the crystallinity ofthe applied pentacene. High conductivity regions 1028 and 1030 and lowconductivity regions 1032, 1034 and 1036 are thus generated within thepentacene layer 1010.

FIGS. 11-16 as discussed above relate to exemplary embodiments ofmethods according to the present invention for fabrication of thedevices shown in FIGS. 1-10, employing pentacene for fabrication of thesemiconductor layer. It is to be understood, however, that thesemiconductor layers of such devices can be fabricated from othermaterials. In further exemplary embodiments according to the presentinvention, a bithiophene such as5,5′-bis-(4-ethylphenyl)2,2′-bithiophene or5,5′-bis-(8-hexylfluorine-1-yl)2,2′-bithiophene is employed as thesemiconductor. In additional exemplary embodiments according to thepresent invention, a thiophene such as sexithiophene or a benzothiophenedimer is employed as the semiconductor. Further exemplary thiophenecompounds that can be used include: 2,5-linked thiophene tetramers,pentamers, and hexamers, either unsubstituted or substituted at theterminal 5 positions with linear alkyl or alkoxyalkyl chains of about 4to about 12 atoms in length; anthradithiophene and terminal dialkylderivatives thereof, including for example dihexylanthradithiophene;regioregular poly (3-hexylthiophene); and co-oligomers of 2,5-linkedthiophene rings and 1,4-linked benzene rings about 5 rings long, eitherunsubstituted or substituted as described for the thiophene oligomers,including for example 1,4-bis(5-(5-hexylthien-2-yl)thien-2-yl)benzene(DHT4Ph). DHT4Ph can be synthesized according to procedures describedfor hexylated 5- and 6-ring compounds in W. Li et al, Chem. Mater., Vol.11, page 458 (1999), using 1,4-diiodobenzene as the source of thebenzene ring. Other substituted and unsubstituted acenes such astetracene and hexacene for example, other bithiophenes, otherthiophenes, phthalocyanines including for example copper phthalocyanineand perfluorinated copper phthalocyanine,naphthalene-1,4,5,8-tetracarboxylic diimide compounds,naphthalene-1,4,5,8-tetracarboxylic dianhydride, and11,11,12,12-tetracyanonaphtho-2,6-quinodimethane, for example, can alsobe used. It is to be understood that the foregoing classes and speciesof semiconductors can be used, if available, in monomeric, oligomericand polymeric forms. See, for example, Dimitrakopoulos et al. U.S. Pat.No. 5,981,970, Bauntech, et al. U.S. Pat. No. 5,625,199, Garnier, et al.U.S. Pat. No. 5,347,144, and Klauck, Hagen et al., “Deposition:Pentacene organic thin-film transistors and ICs,” Solid StateTechnology, Vol. 43, Issue 3, March 2, on pp. 63-75. The entirety of theforegoing patents and article cited in this paragraph are herebyincorporated herein by reference in their entirety. Other organiccompounds that are capable of transporting charge carriers when formedinto a film can also be used. Further, inorganic semiconductors andmixed and hybrid organic and inorganic semiconductors can be used.

Appropriate polymers for fabricating layers and regions that induce highand low conductivity in an adjacent semiconductor layer are selected fora particular semiconductor chosen for use. In one embodiment accordingto the present invention, given a voltage of −50V from source to drainacross a test transistor, the mobility in the high conductivity regionsof the semiconductor is desirably at least about 0.01 cm² Vs, preferablyat least about 0.1 cm²/Vs, and more preferably at least about 1.0cm²/Vs, at room temperature. The structure of the high conductivityregions of the semiconductor desirably has an average crystal grain sizeof at least about 50 nanometers, and an average grain separation of lessthan about 20 angstroms. In one embodiment according to the presentinvention, the high conductivity regions of the semiconductor have anaverage crystal grain size of less than about 500 nanometers. In oneembodiment according to the present invention, the mobility in the lowconductivity regions of the semiconductor is desirably within a rangebetween about 0.3×10⁻⁷ cm²/Vs and about 1.5×10⁻⁵ cm²/Vs at roomtemperature. In one embodiment according to the present invention, theconductivity in the high conductivity regions of the semiconductor is atleast about 100 times as large as the conductivity in the lowconductivity regions of the semiconductor. In another embodimentaccording to the present invention, the average crystal grain sizewithin the high conductivity regions of the semiconductor desirably isat least about 10 times as large the average crystal grain size withinthe low conductivity regions of the semiconductor. In a furtherembodiment according to the present invention, the average separationbetween crystal grains within the low conductivity regions of thesemiconductor desirably is at least about 10 times as large the averageseparation between crystal grains within the high conductivity regionsof the semiconductor.

In one embodiment according to the present invention, a raster scanningmethod is employed to deposit a uniform coating of a selectedsemiconductor material onto a substrate having test regions of selectedhigh and low conductivity inducing polymers. This method providescontrol over the processing conditions and facilitates testing of thecompatibility and performance of the selected materials. The substratecan be provided with test regions of selected high and low conductivityinducing polymers as detailed in steps 1305, 1310 and 1320 discussedabove in connection with FIG. 13, for example. Preparation of gateelectrodes and of source and drain electrodes can be carried out asdetailed above in steps 1315 and 1330 of FIG. 13. A semiconductor layercan be provided in execution of step 1325 shown in exemplary FIG. 13 byemploying the raster scanning method.

According to the raster scanning method, a source of semiconductormaterial is provided, such as pentacene for example. The semiconductormaterial is then heated to a suitable vaporization temperature and issprayed onto the test regions of selected high and low conductivityinducing polymers by the raster scanning method. A spray source such asa nozzle is indexed back and forth in a zigzag raster pattern over thesurfaces of the test regions of selected high and low conductivityinducing polymers in order to systematically cover such surfaces with auniform coating of the selected semiconductor. Control of the volumeover unit time of the heated semiconductor material that is emitted fromthe spray source, and control over the raster pattern and speed, furtherallow control over the thickness of the semiconductor coating layer. Thedistance between the spray source and the surfaces of the test regionsof selected high and low conductivity inducing polymers can becontrolled for uniformity in preparing a test device, and can besystematically varied from one test device to another. In this manner,uniformity of the semiconductor coating in a given test device isencouraged, and the optimum distance between the spray source and thesurfaces of the test regions for the selected materials can readily bedetermined. Further, the temperature of the surfaces of the test regionsof the polymers and of the semiconductor material upon contact with thesurfaces of the test regions of selected high and low conductivityinducing polymers can be controlled in order to adjust the resultingcrystallinity of the semiconductor coating.

FIGS. 11-16 as discussed above relate to exemplary and non limitingembodiments of methods according to the present invention. Othersuitable methods for making the exemplary devices shown in FIGS. 1-10can also be used. For example, other processes can be used for providingthe high and low conductivity inducing polymer layers and regions on theinsulating substrates. Such other processes can include, for example,ink jet printing, vapor deposition, liquid film casting, spin casting,evaporative film casting, and thermal transfer imaging. High and lowconductivity inducing polymer layers can be patterned, for example, byphotolithography and oxygen plasma etching. Continuous coatings can beconverted into defined layer regions by laser ablation, for example.Further processes that may be useful in making the exemplary devicesshown in FIGS. 1-10 are disclosed in U.S. patent application Ser. No.______, filed concurrently herewith, entitled “Semiconductor Layers withRoughness Patterning”, assigned to Lucent Technologies Inc., theentirety of which is hereby incorporated by reference herein.

In one embodiment according to the present invention, high and lowconductivity inducing polymer layers and regions are provided oninsulating substrates by a process comprising laser induced thermaltransfer imaging. For example, a laser can be used to induce thepatterned transfer of a high or low conductivity inducing polymermaterial from a donor film to a receiver film. Each type of polymer,inducing either high or low conductivity, typically is individuallyprinted in a separate printing step, and one donor film at a time isprinted. In another embodiment according to the present invention,multiple polymers are simultaneously printed. A suitable donor film maycomprise a MYLAR polyethylene terephthalate base having a thickness of 2mils, having a semitransparent coating of sputtered chromium, nickel oraluminum with a thickness that allows transmittance of about 50% ofvisible light. The desired high or low conductivity inducing polymer tobe transfer printed is then suitably coated onto the sputtered metalsurface of the donor film. The receiver film may be constituted by afilm of the selected insulating substrate material, and may comprise asupportive backing for the substrate that can later be removed. Thedonor and receiver films are then assembled together with the desiredhigh or low conductivity inducing polymer facing the substrate. Theassembled films are then sized and fitted onto a printer cylinder withthe donor film facing out. Alternatively, if the receiver film istransparent then the receiver film can face out. Typically, the receiverfilm is wrapped around the drum. Then the donor film is wrapped aroundthe receiver. The laser is directed in through the back of the donorfilm. In this manner, a donor film can be unloaded and another donorfilm can then be loaded in its place. The printer cylinder may, forexample, have a diameter of about 14 inches.

A laser head is provided adjacent to the printer cylinder, aimed todirect laser light onto the cylinder surface through the assembledfilms. The laser head may, for example, include 200 lasers having acollective beam width of 500 microns, providing a resolution of 2×5microns. The exemplary laser spot size has a length of 5 microns acrossthe head, and a width of 2 microns in the direction of printer cylinderrotation. The laser head includes a lead screw for guiding the laserhead over the longitudinal axis of the printer cylinder. In operation ofthe printer, the cylinder turns at a selected rotation rate per unittime, and the lead screw systematically advances the laser head over theprinter cylinder surface in a barber pole fashion. The lasers within thelaser head can be individually energized for precise pattern control. Asthe laser head is guided over the surface of the printer cylinder, laserlight is directed in a precise desired pattern corresponding to thedesired high or low conductivity inducing polymer layers or regions onthe insulating substrate. Typically, the precise pattern is computergenerated. In the precise areas where laser energy enters the donorfilm, the high or low conductivity inducing polymer is transferred ontothe insulating substrate. Fine accuracy of the printing pattern isneeded. This accuracy can be achieved by proper programming of thecomputer guidance systems. Further advantageous embodiments of laserinduced thermal transfer imaging processes that can be employed inpractice of various aspects of the present invention are disclosed inU.S. patent application Ser. No. ______, filed concurrently herewith,entitled “Method for Increasing Mobility of Vapor Deposited Pentacene.”This patent application is assigned to E. I. du Pont de Nemours andCompany, docket No. CL-2447, and is hereby incorporated by referenceherein in its entirety.

Processes and apparatus relating to laser induced thermal transferimaging are disclosed in the following patent documents for example,which are hereby incorporated by reference herein in their entirety:Blanchet-Fincher U.S. Pat. No. 5,192,580; Blanchet-Fincher U.S. Pat. No.5,288,528; Blanchet-Fincher U.S. Pat. No. 5,523,192; Blanchet-FincherU.S. Pat. No. 5,563,019; Blanchet-Fincher U.S. Pat. No. 5,766,819;Blanchet-Fincher U.S. Pat. No. 5,840,463; Blancher-Fincher U.S. Pat. No.6,143,451; Blancher-Fincher et al. U.S. Pat. No. 6,146,792;Blanchet-Fincher U.S. Patent Pub. No. 2002/0149315; Blanchet-Fincher etal. PCT published application WO 01/87634 A2 dated 11/22/2001;Blanchet-Fincher et al. PCT published application WO 02/08801 A1 datedJan. 31, 2002; and Blanchet-Fincher et al. PCT published application WO02/092352 A1 dated Nov. 21, 2002. Apparatus for carrying out laserinduced thermal transfer imaging are commercially available from CreoInc., 3700 Gilmore Way, Burnaby, British Columbia, V5G 4M1, Canada. Forexample, Creo Trendsetter thermal platesetters can be employed.

Optimization of laser induced thermal transfer imaging processesincludes proper formulation of the polymer materials to be transferprinted. Variables to be addressed regarding the polymers include glasstransition temperature (Tg) and melt viscosity. For example, polymershaving a glass transition temperature within a range between about −20°C. and about 100° C. may provide adequate film stability while avoidingexcessive film brittleness. Further for example, polymers having a meltviscosity within a range between about 10 centipoise (CPS) and about 100CPS may provide adequate workability for coating onto a donor film whilehaving adequate body to form a layer of a desired thickness. Polymermelt viscosity generally increases with increasing average molecularweight. A desired film thickness may be about one micron, for example.Variables to be addressed regarding solvent systems for the polymersinclude substrate wetting, drying performance, and polymer dispersion ordissolution. Suitable solvent systems are able to wet the substratesurfaces of both donor and receiver films, are able to evaporate toyield a uniform dry film having a surface area of at least about asquare foot within a reasonable working time, allow preparation of apolymer layer of a desired thickness, and either disperse or dissolvethe polymer. A given solvent wets a substrate if the contact angle of adrop of solvent on the substrate is less than about 90°. Organicsolvents or surfactants added to aqueous systems are generally needed inorder to wet the sputtered metal surface of the donor film. Variables tobe addressed regarding the resulting polymer films include strain tobreak, surface energy and cohesive energy. In order for the polymercoating to be discontinuously transferred from the donor film to therecipient film, the polymer coating must be able to cleanly breakwithout stretching or distortion at the boundaries defined by the laserhead as it is indexed over the cylinder surface. Various materials canbe added to the polymers and solvent system of a composition to be usedin furtherance of such optimization. For example, copolymers, coatingaids, plasticizers, flow additives, slip agents, anti-halation agents,antistatic agents, surfactants, dispersants, and other agents known tobe used in the formulation of coatings may be added.

A series of test transistors were fabricated in accordance with thepresent invention and tested for conductivity. For the preparation ofeach test transistor, a silicon dioxide glass slide was provided toserve as the insulating substrate. A surface of the silicon dioxideslide was thoroughly cleaned in the same manner as discussed above inconnection with FIG. 11. Gate electrodes formed from aluminum were thenprovided on the insulating substrate. A selected polymer layer was thenspin coated onto the insulating substrate, and regions of the layer wereremoved by swabbing with a suitable solvent. A layer of a selectedsemiconductor was then provided on the layer regions and on the exposedportions of the silicon dioxide glass slide. In order to provide thesemiconductor layer, the semiconductor material was heated to a suitablevaporization temperature and was deposited onto the test regions of theselected polymers by the bell jar evaporator method. The glass slide wasplaced in a suitable vacuum chamber such as a bell jar, which was thenevacuated. A source of the semiconductor was also placed in the vacuumchamber and heated to vaporize and deposit the semiconductor over thetest regions. Gold source and drain electrodes were then provided on thesemiconductor layer in alignment over the gate electrodes, prepared inthe same manner as was discussed above in regard to FIG. 11.

FIG. 17 shows, in Table 1, the results of 11 series of trials that werecarried out. The semiconductor in series 1-5 was pentacene. Thesemiconductor in series 6-8 was5,5′-bis-(4-ethylphenyl)2,2′-bithiophene, abbreviated as 2PTTP2. Thesemiconductor in series 9-11 was5,5′-bis-(8-hexylfluorine-1-yl)2,2′-bithiophene, abbreviated as DHFTTF.The selected polymer in series 1, 7 and 10 was poly(4-vinylpyridine),abbreviated as PVPYR. The selected polymer in series 2, 8 and 11 waspoly(vinylidene difluoride-co-methyl-vinyl-ether), abbreviated asPVDFMVE. The selected polymer in series 3, 6 and 9 was poly(n-butylmethacrylate), abbreviated as PBMA. The selected polymer in series 4 and5 was poly(para-vinylphenol), abbreviated as PVPH. Table 1 indicates thequantity of samples within each of the eleven series of transistors thatwere tested. The mobility within regions of the semiconductor layers incontact with the selected polymers was measured and reported in cm²/Vs.The standard deviation of such mobility among all samples was alsoreported. The threshold voltage in volts was measured and reported,together with the standard deviation of such threshold voltage among allsamples. The on/off ratio of conductivity with a zero gate current wasmeasured and reported. The subthreshold swing voltage per decade wasmeasured and reported. The subthreshold swing voltage per decade is ameasure of the gate voltage change required to increase the currentflowing in the test transistors by a factor of ten. In trial series 1-3and 5, the silicon dioxide slides were heated to the indicatedtemperatures during semiconductor deposition. In the other trial series,the slides were at ambient temperature during such deposition. The testmeasurements were obtained at ambient temperature.

The test results in Table 1 showed in series 1-5 that the conductivityfor a pentacene semiconductor layer was relatively high when depositedover poly(4-vinylpyridine) or poly(para-vinylphenol), and relatively lowwhen deposited over poly(vinylidene difluoride-co-methyl-vinyl-ether) orpoly(n-butyl methacrylate). The test results further showed in series6-8 that the conductivity for a 5,5′-bis-(4-ethylphenyl)2,2′-bithiophenesemiconductor layer was relatively high when deposited overpoly(4-vinylpyridine), and relatively low when deposited overpoly(vinylidene difluoride-co-methyl-vinyl-ether) or poly(n-butylmethacrylate). The test results also showed in series 9-11 that theconductivity for a 5,5′-bis-(8-hexylfluorine-1-yl)2,2′-bithiophenesemiconductor layer was relatively high when deposited overpoly(4-vinylpyridine), and relatively low when deposited overpoly(vinylidene difluoride-co-methyl-vinyl-ether) or poly(n-butylmethacrylate).

While the present invention has been disclosed in the context of variousaspects of presently preferred embodiments, it will be recognized thatthe invention may be suitably applied to other environments consistentwith the claims which follow.

1-18. (canceled)
 19. A method of making a semiconductor apparatus,comprising the steps of: forming a substrate having a substrate surface;forming a layer of a first material overlying a first region of saidsubstrate surface; forming a layer of a second material overlying asecond region of said substrate surface; and forming a layer of asemiconductor overlying said layer of first material and overlying saidlayer of second material; a first region of said layer of semiconductor,overlying said layer of first material and having a first conductivity;a second region of said layer of semiconductor, overlying said layer ofsecond material and having a second conductivity; said firstconductivity being substantially different from said secondconductivity.
 20. (canceled)
 21. The method of claim 19, in which saidlayer of first material overlies said second region of said substratesurface.
 22. The method of claim 19, in which said first material isselected from the group consisting of: poly(para-vinyl phenol),poly(4-vinylpyridine), poly(2-vinylnaphthalene), poly(meta-vinylphenol), poly(ortho-vinyl phenol), poly(para-vinylphenol)-co-2-hydroxyethylmethacrylate, poly(2-vinylpyridine),poly(2-vinylnaphthalene-co-2-ethylhexyl acrylate,poly(1-vinylnaphthalene), and blends.
 23. The method of claim 19, inwhich said second material is selected from the group consisting of:poly(n-butyl methacrylate), poly(vinylidene difluoride-co-methyl vinylether), polystyrene, poly(p-methoxystyrene), poly(vinylidenedifluoride), poly(vinyl acetate), poly(vinyl propionate), poly(methoxyacetate), poly(n-propyl methacrylate), poly(isopropyl methacrylate),poly(n-pentyl methacrylate), poly(vinylidene difluoride-co-ethyl vinylether), poly(vinylidene difluoride-co-propyl vinyl ether),poly(dimethylaminoethyl methacrylate), poly(dimethylaminopropylmethacrylate), poly(aminopropyl methacrylate), poly(diethylaminoethylmethacrylate), and blends. 24-26. (canceled)
 27. The method of claim 19,in which said first material is a polymer.
 28. The method of claim 19,in which said second material is a polymer.
 29. The method of claim 19,further including: forming a first gate electrode; forming a firstsource electrode; and forming a first drain electrode; spacing apartsaid first source and drain electrodes in conductive contact with afirst channel portion of either said first or said second region of saidlayer of semiconductor, and positioning said first gate electrode tocontrol a conductivity of said first channel portion.
 30. A method ofmaking a semiconductor apparatus, comprising the steps of: forming asubstrate having a substrate surface; forming a layer of a firstmaterial overlying a first region of said substrate surface; forming alayer of a second material overlying a second region of said substratesurface; and forming a layer of a semiconductor overlying said layer offirst material and overlying said layer of second material; a firstregion of said layer of semiconductor overlying said layer of firstmaterial and including crystal grains having a first average crystalgrain size, a second region of said layer of semiconductor overlyingsaid layer of second material and including crystal grains having asecond average crystal grain size, said first average crystal grain sizebeing substantially different from said second average crystal grainsize.
 31. The method of claim 30, in which said layer of first materialoverlies said second region of said substrate surface.
 32. The method ofclaim 30, in which said first material is a polymer.
 33. The method ofclaim 32, in which said first material is selected from the groupconsisting of: poly(para-vinyl phenol), poly(4-vinylpyridine),poly(2-vinylnaphthalene), poly(meta-vinyl phenol), poly(ortho-vinylphenol), poly(para-vinylphenol)-co-2-hydroxyethylmethacrylate[[poly(para-vinylphenol)-co-2-hydroxyethylmethacrylate]], poly(2-vinylpyridine),poly(2-vinylnaphthalene-co-2-ethylhexyl acrylate,poly(1-vinylnaphthalene), and blends.
 34. The method of claim 30, inwhich said second material is a polymer.
 35. The method of claim 34, inwhich said second material is selected from the group consisting of:poly(n-butyl methacrylate), poly(vinylidene difluoride-co-methyl vinylether), polystyrene, poly(p-methoxystyrene), poly(vinylidenedifluoride), poly(vinyl acetate), poly(vinyl propionate), poly(methoxyacetate), poly(n-propyl methacrylate), poly(isopropyl methacrylate),poly(n-pentyl methacrylate), poly(vinylidene difluoride-co-ethyl vinylether), poly(vinylidene difluoride-co-propyl vinyl ether),poly(dimethylaminoethyl methacrylate), poly(dimethylaminopropylmethacrylate), poly(aminopropyl methacrylate), poly(diethylaminoethylmethacrylate), and blends.
 36. The method of claim 30, furtherincluding: forming a first gate electrode; forming a first sourceelectrode; and forming a first drain electrode; spacing apart said firstsource and drain electrodes in conductive contact with a first channelportion of either said first or said second region of said layer ofsemiconductor, and positioning said first gate electrode to control aconductivity of said first channel portion.
 37. A method of making asemiconductor apparatus, comprising the steps of: forming a substratehaving a substrate surface; forming a layer of a first materialoverlying a first region of said substrate surface; forming a layer of asecond material overlying a second region of said substrate surface; andforming a layer of a semiconductor overlying said layer of firstmaterial and overlying said layer of second material; a first region ofsaid layer of semiconductor overlying said layer of first material andincluding crystal grains having a first average crystal grain size, asecond region of said layer of semiconductor overlying said layer ofsecond material and including crystal grains having a second averagecrystal grain size, said first average crystal grain size beingsubstantially larger than said second average crystal grain size. 38.The method of claim 37, in which said layer of first material overliessaid second region of said substrate surface.
 39. The method of claim37, in which said first material is a polymer.
 40. The method of claim39, in which said first material is selected from the group consistingof: poly(para-vinyl phenol), poly(4-vinylpyridine),poly(2-vinylnaphthalene), poly(meta-vinyl phenol), poly(ortho-vinylphenol), poly(para-vinylphenol)-co-2-hydroxyethylmethacrylate[[poly(para-vinylphenol)-co-2-hydroxyethylmethac-rylate]], poly(2-vinylpyridine),poly(2-vinylnaphthalene-co-2-ethylhexyl acrylate,poly(1-vinylnaphthalene), and blends.
 41. The method of claim 37, inwhich said second material is a polymer.
 42. The method of claim 37,further including: forming a first gate electrode; forming a firstsource electrode; and forming a first drain electrode; spacing apartsaid first source and drain electrodes in conductive contact with afirst channel portion of either said first or said second region of saidlayer of semiconductor, and positioning said first gate electrode tocontrol a conductivity of said first channel portion.